Optical Recording Materials Based on Photoisomerization of Guest Molecules of a Polymeric Crystalline Host Phase

Abstract

Optical recording technology has a major advantage over other recording technologies, namely, that reading and writing of data is accomplished by light, so that no physical contact between the media and the optical head occurs. The storage capacity of these optical media (e.g., disks) is limited by the size of the smallest marks on their surfaces that can be read by the wavelength of light used. In this communication, we present a possible data storage system with molecular-sized (» 200 3 ) marks that also give, in principle, the possibility to record information depthwise, rather than just on the material surface.Photoreactions of organic dyes, generally added or covalently bonded to stable and transparent polymeric materials, have been widely used as means of recording optical data. In particular, photoisomerizations are often preferred to other reactions (like, e.g., photopolymerizations) due to the negligible dimensional changes associated with recording. These photoisomerization reactions have to cause some change in the optical properties of the exposed regions of the opticalrecording material, such as changes in the absorption or fluorescence spectrum, or the refractive index.It is well known that norbornadiene and its derivatives (N, see Scheme 1; h: Planck's constant; m: radiation frequency; k: radiation wavelength) are easily photoisomerized into quadricyclane and its derivatives (Q, see Scheme 1) upon UV irradiation. Photoisomerization of N has been widely investigated in organic solutions [1] as well as in aqueous media [2] and, more recently, in organic polymers. [3,4] In particular, polymeric materials containing N derivatives, both as covalently bonded pendant groups [3] or simply added to transparent amorphous phases, [4] have been investigated for use as optical waveguides (utilizing photoinduced refractive-index changes) and for data storage.In recent years, we have extensively studied a nanoporous crystalline phase (the so-called d phase) of syndiotactic polystyrene (s-PS), which has two identical cavities and eight styrene monomeric units per unit cell, [5] and which is promising for applications in chemical separation, air/water purification, and sensorics. [6] In fact, it rapidly and selectively absorbs (both from the gas phase [6a,e±g] and aqueous solutions [6b,d] ) suitable guest molecules even at very low activities, generally absorbing only one isolated guest molecule per cavity. [5,7] Moreover, studies of guest-desorption kinetics [6c] and of gas transport [6g] on s-PS films have shown that the guest diffusivity in the d phase is much lower than in the amorphous phase. The latter feature is quite relevant since it assures a higher stability of the doping of this crystalline phase with respect to the usual doping of amorphous phases. We have included N as the isolated guest of the host d crystalline phase of robust s-PS polymer films, and we have achieved efficient valence photoisomerization of N to Q in this polymeric crystalline phase. In fact, it will be shown that no...

Understanding at molecular level of nanoporous and co-crystalline materials based on syndiotactic polystyrene

“…On this basis, films presenting s-PS/active guest co-crystals have been proposed as advanced materials, mainly for optical applications (e.g. fluorescent, photo-reactive, chromophore and nonlinear optical materials) [57][58][59][60][61][62][63].…”

The Impact of Imaging Techniques Based on Vibrational Spectroscopy on the Molecular Characterization of Syndiotactic Polystyrene Co-Crystals

“…Furthermore, it was shown that both NBD and QDC possess positional and orientational order with respect to the polymeric host crystallographic axes (20). It was demonstrated (20) that NBD can form stable clathrate and/or intercalate phases within s-PS films and that photoisomerization of NBD to QDC can be easily achieved in these films.…”

Polymer co-crystalline films for photonics

“…In some recent studies it has been reported that norbornadiene could form a clathrate phase with sPS and that efficient valence photoisomerization of N to Q in the crystalline phase can be achieved [30,31].…”